Posts Tagged ‘junit’

Unit Test Private Java Methods using Reflection

Thursday, May 5th, 2011


I realise that the thought of Unit Testing private methods in Java classes can be like a red rag to a bull for some people and I understand the arguments.

Therefore, I present the following as a “how to”, not a moral argument for or against!


The class under test

public class Product() {
    private String privateMethod(String id) {
    //Do something private
    return "product_" + id;

The (Reflection Based) Unit Test

import java.lang.reflect.Method;

import static org.junit.Assert.*;
import org.junit.Test;

public class ProductTest {
    private Product product; // the class under test
    private Method m;
    private static String METHOD_NAME = "privateMethod";
    private Class[] parameterTypes;
    private Object[] parameters;

    public void setUp() throws Exception {
        product = new Product();
        parameterTypes = new Class[1];
        parameterTypes[0] = java.lang.String.class;
        m = product.getClass().getDeclaredMethod(METHOD_NAME, parameterTypes);
        parameters = new Object[1];

    public void testPrivateMethod() throws Exception {
        parameters[0] = "someIdentifier";
        String result = (String) m.invoke(product, parameters); 
        //Do your assertions


I’ve since been told that if dp4j.jar is in the classpath at compile-time, it will inject the necessary reflection to make this work. I haven’t had time to try this yet so YMMV.

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Posted in Development, How to's | No Comments »

Unit Testing Validation in Annotation Based Validating Spring Beans

Friday, April 22nd, 2011


I added validation, via annotations, to a Spring “Model” bean. I needed someway to Unit Test this validation, without running the container and without initialising the Spring context.

The bean (simplified)


import javax.validation.constraints.NotNull;
import javax.validation.constraints.Pattern;
import javax.validation.constraints.Size;

public final class ProductModel {
    @Pattern(regexp="[^\n^\t^\r]+", message="Long Name must not contain New Lines, Carriage Returns or Tabs")
    private String longName;

    private String shortName;

    // rest snipped for brevity

The Unit Test


import java.util.Set;

import javax.validation.ConstraintViolation;

import junit.framework.Assert;

import org.hibernate.validator.HibernateValidator;
import org.junit.Before;
import org.junit.Test;
import org.springframework.validation.beanvalidation.LocalValidatorFactoryBean;

public class Temp {
    private LocalValidatorFactoryBean localValidatorFactory;
    public void setup() {
        localValidatorFactory = new LocalValidatorFactoryBean();
    public void testLongNameWithInvalidCharCausesValidationError() {
        final ProductModel productModel = new ProductModel();
        productModel.setLongName("A long name with\t a Tab character");
    	Set<ConstraintViolation<ProductModel>> constraintViolations = localValidatorFactory.validate(productModel);
    	Assert.assertTrue("Expected validation error not found", constraintViolations.size() == 1);


It actually took me a few hours to work the above test out (simple as it is). If I hadn’t stumbled upon these Spring Unit Tests, I might never have got it.

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Posted in Spring | 3 Comments »

JUnit 4 Test Class with annotations

Tuesday, June 8th, 2010

A simple example of a JUnit 4 Test class marked up with annotations.

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Posted in Examples | No Comments »